In order to impart satisfactory grip performance on wet roads to the tires, it is known to provide each tread with a tread pattern formed of ribs of circumferential or longitudinal general orientation (that is to say, which may zigzag around this direction) and to provide these ribs with a plurality of incisions of low width compared with the width of the grooves (as a general rule, the average width of the incisions is at most 2 mm); these incisions are generally of transverse orientation, that is to say that the direction formed by a straight line passing through the end points of these incisions forms an angle other than 0° with the circumferential direction (generally greater than 40°). Each transverse incision may extend over only part of or over the entire useful thickness of the tread (by definition, the useful thickness of a tread corresponds to the tread thickness which it is possible to wear down while remaining within the legal regulations in force). Of course, the performance obtained is also linked to the nature of the materials selected for a tread: application to tires for heavy vehicles requires in particular materials having a wear performance compatible with the intended traveling distances.
However, conventional treads for tires for heavy vehicles comprising numerous incisions begin more or less quickly to exhibit wear located in the vicinity of the ridges of said incisions when used. “Localized wear” is to be understood here to mean that the wear does not uniformly affect the entire running surface of the tread but that there is more pronounced wear on some of parts of said running surface.
Although such wear is not detrimental from the point of view of performance during travel, it nevertheless remains that the time when it becomes necessary either to change the tire or to renew the tread may be reached more rapidly.
This wear is linked partly to a reduction in rigidity of the tread, this reduction in rigidity being in part linked to the possibility of the facing faces of material defining each incision sliding relative to each other when entering into contact with the roadway.
It has been proposed, in particular in Patent EP 768958 B1 (corresponding to Lagnier U.S. Pat. No. 5,783,002), to provide means for blocking the relative movements of the faces of material defining each incision. One embodiment of such blocking means consists of providing the faces with a plurality of undulations which engage with one another, these undulations extending in at least one direction. In order to limit or even block the relative movements between two faces defining an incision in the direction of the thickness of the tread (that is to say in a substantially radial direction when the tread is fitted on a tire), undulations are produced in the direction perpendicular to said direction.
It has however been noted that the wear performance could be improved further while retaining excellent grip performance.
There is a need for a tread pattern for a tire which is formed essentially of circumferential ribs provided with a plurality of incisions, of an average width of less than 2 mm, creating a large number of ridges and a great length of ridges, these incisions defining a plurality of rubber elements the facing walls of which block each other with virtually instantaneous effectiveness (that is to say with a very substantially reduced or even zero delay) and which do not generate localized wear (termed “irregular wear”).